I have set up a reverse-ssh appliance with a Raspberry-Pi for use at a customer site to connect to a piece of equipment I have to support via a USB-to-RS232 adapter. I've cleared this with the customer's IT staff, and the appliance is already configured, tested and working fine.
But in the interest of hardening it from local-net access, I would like to restrict logins to only allow login through the reverse SSH tunnel, and not allow anyone on the local customer's network to login.
The outgoing reverse-ssh connection uses a 4096-bit keyfile with no password to connect to the server, but I still see a user/password prompt when I connect back from the server to the Pi through the reverse ssh connection. That's not a problem for me, but I was just concerned about limiting the ability of anyone locally to log in with a local telnet or ssh. I already have a good password on the only active account, so I doubt that anyone would manage to log in anyway.
It would be good if it still allowed logins on the local machine with an attached USB keyboard for maintenance purposes, but that's not mandatory. The device is inside a locked metal enclosure in a locked room, so unauthorized physical access is not a great concern. I just want to lock out local-network access to telnet & ssh logins while still allowing ssh logins through the reverse ssh tunnel.